A giant panda gave birth to a cub at the US National Zoo, but no one is yet sure about the father's identity as she was impregnated using sperm from two males.

Mei Xiang gave birth to the tiny pinkish-white cub just after 5.30pm on Friday and the event was shown live on two internet webcams from the panda's den. She picked up the cub and cradled it, then began nursing.

The sex of the cub remains unknown for now.

The birth was the third for Mei Xiang, who along with her male counterpart Tian Tian is on loan to the US zoo from China.

The two pandas attempted to conceive naturally during their once-a-year mating ritual this winter. But after reproductive specialists determined that bid was unsuccessful, they performed artificial insemination using sperm samples from both Tian Tian and another male panda, Gao Gao, who lives at the San Diego Zoo.

"We had never tried that before, normally Mei Xiang was inseminated with the semen of only one male," reproductive scientist Pierre Comizzoli said.

The baby's daddy will be revealed after a DNA test is conducted, possibly as early as in the next day or two, the zoo said.

The DNA sample will be taken during the cub's first neonatal exam, along with measurements of its weight and overall health.

A cub born to Mei Xiang last year died six days later, due to liver and lung problems. Mei Xiang and Tian Tian's son, Tai Shan, now lives at the Bifengxia Panda Base in China.

This article appeared in the South China Morning Post print edition as A new panda cub, but who's the dad?